An exemplary method for realizing mobile communication is MIP (Mobile Internet Protocol) described in RFC3344. The RFC3344 is introduced in “IP Mobility support for IPv4”, RFC3344, August 2002, Network Working Group, URL:http://www.ietf.org/rfc/rfc3344 (browsed on Jan. 17, 2008).
In the MIP, an MN (Mobile Node) that is a mobile node transmits a registration request signal for association of a CoA (Care-of Address) that is an address acquired from a connection destination network with an HoA (Home Address) fixedly assigned to the MN regardless of the network to which the MN is connected, to an HA (Home Agent) that is an administration server, at the time of a network connection and network migration as well as after a predetermined time.
In accordance with the registration request signal, the HA holds the correspondence relationship between the HoA and CoA and receives, by proxy, traffic destined for the HoA by the MN. The HA encapsulates the traffic and then transfers the encapsulated traffic to the CoA. Thus, even after migration, the MN can continue to receive packets transmitted to the HoA by the MN, achieving mobile communication.
Here, in connection with the use of the CoA, the RFC3344 specifies two types of methods, that is, a method utilizing the CoA assigned to the MN itself (Co-located CoA mode) and a method in which the CoA held by an FA (Foreign Agent) that is a transfer node is shared by a plurality of MNs (FA mode). In the FA mode, the registration request signal transmitted by the MN is transmitted to the HA via the FA. A registration reply signal that is a reply to the registration request signal is also transmitted to the MN via the FA.
The IETF (Internet Engineering Task Force) is now examining a similar technique based on a protocol called a proxy mobile IP (PMIP). In this technique, a node called a PMIP client or a MAG (Mobile Access Gateway) transmits the registration request signal to a node serving as an HA, instead of a mobile node that has migrated into an area covered by the PMIP client or the MAG.
The PMIP is introduced in “WiMax Forum/3GPP2 Proxy Mobile IPv4”, Sep. 20, 2007, URL:http://tools.ietforg/html/draft-leung-mip4-proxy-mode-4 (browsed on Jan. 17, 2008) and “Proxy Mobile IPv6”, Nov. 4, 2007, NETLMM WG, URL:http://toolsietforg/html/draft-letf-netImm-proxymip6-07 (browsed on Jan. 17, 2008).